(1) Field of the Invention
The invention concerns a novel process for purifying large batches of impure AT-125. The process involves converting impure AT-125 to a derivative from which pure AT-125 can be generated. The invention also includes novel analogs prepared and used in the process. Some of the analogs also have antitumor and antimicrobial activity.
(2) Description of the prior art
AT-125 which can be represented by structure of formula I ##STR1## and a microbiological process for producing it are disclosed and claimed in U.S. Pat. Nos. 3,856,807 and 3,878,047, respectively. These patents also disclose the antitumor and antimicrobial activities of AT-125.
The concept of separating refractory mixtures or purifying a contaminated material via a derivative from which the desired compound(s) can be regenerated is not novel. As an example, biotin antimetabolites, .alpha.-methylbiotin, .alpha.-dehydrobiotin, and .alpha.-methyldethiobiotin were separated as their phenacyl esters [Martin et al., Tetrahedron Letters pp. 3791-3794 (1971)].
Background information on preparation and removal of phthalimido, p-nitrobenzyl esters of carbobenzyloxy, and carbotertbutyloxy derivatives of amino acids is found in R. A. Boissonnas chapter, "Selectively Removable Amino Protective Groups used in the Synthesis of Peptides," In: Advances in Organic Chemistry, 3:159-190 (1963), editors Raphael et al., Interscience Publishers.
Background information on the 9-fluorenylmethoxy carbonyl amino protecting group is found in J. Org. Chem. 37:3404-3409 (1972) (Carpino et al.).
Information on the t-butoxy carbonyl amino protecting group described is ALDRICH'S technical information on BOC-ON, September, 1976.
Chromatographic separation (conventional and high performance liquid chromatography (HPLC)) of AT-125 mixtures have been attempted and although chromatographic separation is feasible, solubility limitations make large-scale application difficult and inconvenient.
However, the combination of very low solubility in organic solvents and similar chromatographic mobilities of components in the AT-125 mixture prepared as described in U.S. Pat. Nos. 3,856,807 and 3,878,047 has made final purification of AT-125 extremely difficult on a large scale. Recrystallization from methanol accomplished little; an improved crystallization procedure from aqueous secondary butanol removed some contaminants but left others. Countercurrent distribution afforded partial resolution and some pure material but the process suffered from solubility limitations and emulsions and offered little hope for large-scale application.